Known hydraulically-actuated fuel injection systems and/or components are shown, for example, in U.S. Pat. Nos. 5,687,693 and 5,738,075 issued to Chen and Hafner et al. on Nov. 18, 1997 and Apr. 14, 1998, respectfully.
In these hydraulically actuated fuel injectors, a spring biased needle check opens to commence fuel injection when pressure is raised by an intensifier piston/plunger assembly to a valve opening pressure. The intensifier piston is acted upon by a relatively high pressure actuation fluid, such as engine lubricating oil, when an actuator driven actuation fluid control valve, for example a solenoid driven actuation fluid control valve, opens the injector's high pressure inlet.
Injection is ended by operating the actuator to release pressure above the intensifier piston. This in turn causes a drop in fuel pressure causing the needle check to close under the action of its return spring and end injection.
Recently, Caterpillar Inc. has developed a new generation of fuel injectors, such as the HEUI-B.TM. fuel injector, that feature direct control of the spring biased needle check valve. In these fuel injectors, even when fuel pressure has been raised by the intensifier piston to the valve opening pressure, the check valve can be kept shut (or quickly shut if it is open) by applying high pressure hydraulic fluid directly to the back of the needle check valve.
A critical component of both types of hydraulically actuated fuel injector is the actuation fluid control valve, which admits the high pressure actuating fluid to the injector. In the HEUI-B.TM. type injectors the actuation fluid control valve is especially critical because it must be able to control both the intensifier piston and the check valve.
In a yet-to-be-released HEUI-B.TM. fuel injector described in co-pending patent application Ser. No. 09/1358,990 filed Jul. 22, 1999 and entitled "Hydraulically Actuated Fuel Injector with Seated Pin Actuator" a two-way valve is used both to apply direct control on the check valve, and also to operate the spool valve that controls actuation of an intensifier piston.
Embodiments of the HEUI-B.TM. type injectors with a seated pin actuator valve are described below with reference to FIGS. 1-3. The fuel injector 10 utilizes an actuation fluid control valve including a single attractive two-way solenoid 12. An armature assembly includes an actuation valve member 14 attached with an armature 16. The solenoid 12 pulls the armature assembly upward in an actuator bore 18. An actuator spring 20 biases the armature 16 and the attached actuation valve member 14 downward.
High-pressure actuation fluid from a hydraulic fluid source, such as a common rail (not shown) that feeds a number of fuel injectors for example, enters the fuel injector 10 through an actuation fluid inlet 22. A fluid entry chamber 24 (FIG. 2) in the actuation fluid control valve is always exposed to the high pressure actuation fluid, as is an upper end hydraulic surface 26 (FIG. 3) of a spool valve member 28 that is slidable up and down in a spool valve bore 30.
The actuation fluid control valve operates as follows. At a first position the solenoid 12 is de-energized and the actuator spring 20 pushes the valve member 14 downward to mate with a drain seat 32. In this position high-pressure actuation fluid flows from the fluid entry chamber 24 into a check control cavity 34.
The high-pressure actuation fluid in the check control cavity 34 flows down into a check control chamber 36, at which time the high pressure actuation fluid together with a check spring 38 act on a closing hydraulic surface 40 of a check valve member 42 to close nozzle outlets 44 of a nozzle 46. This keeps fuel in a nozzle chamber 48 from being injected into an engine for example.
The high pressure actuation fluid in the check control cavity 34 also flows into a side passage 50 where it acts against a lower end hydraulic surface 52 of the spool valve member 28. This balances the hydraulic fluid pressure against the upper end hydraulic surface 26 of the spool valve member 28, so that a spool valve spring 54 can keep the spool valve member 28 in an up position that closes off an intensifier control passage 56 from the source of high pressure actuation fluid, while opening the intensifier control passage 56 to a low pressure hydraulic fluid drain 58.
When the solenoid 12 is energized it pulls the actuation valve member 14 upward against an inlet seat 60. This closes off the check control cavity 34 from the source of high-pressure hydraulic fluid in the fluid entry chamber 24, while opening the check control cavity 34 to a low-pressure actuator fluid drain 62. This reduces fluid pressure in the check control chamber 36 so that only the force of the check spring 38 is acting on the closing hydraulic surface 40 of the check valve member 42.
This also reduces fluid pressure against the lower end hydraulic surface 52 of the spool valve member 28. When this happens, the force of the high pressure actuation fluid on the upper end hydraulic surface 26 of the spool valve member 28 overcomes the force of the spool valve spring 54 and pushes the spool valve member 28 downward. This closes off the intensifier control passage 56 from the hydraulic fluid drain 58, while opening the intensifier control passage 56 to the source of high-pressure actuation fluid.
The high pressure actuation fluid in the intensifier control passage 56 pushes down on an intensifier piston 64, pressurizing fuel in a fuel pressurization chamber 66 that has entered from a fuel inlet 68 connected to a source of low pressure fuel (not shown). The highly pressurized fuel flows through a connection passage 70 to the nozzle chamber 48 until fuel pressure in the nozzle chamber 48 is high enough to overcome the bias of the check spring 38 and push the check valve member 42 upward, which opens the nozzle outlets 44 and allows the fuel in the nozzle chamber 48 to be injected from the fuel injector 10.
To terminate fuel injection the actuator 12 is de-energized, allowing the actuator spring 20 to move the actuation valve member 14 back to the first position. In this position the check control cavity 34 is closed off from the actuator fluid drain 62, and is fluidly connected to high-pressure actuation fluid from the actuation fluid inlet 22. This causes high pressure actuation fluid to be applied to the lower end hydraulic surface 52 of the spool valve member 28, once again balancing the force of the high pressure actuation fluid against the upper end hydraulic surface 26 of the spool valve member 28.
The bias provided by the spool valve spring 54 can now move the spool valve member 28 upward to cut off the supply of high pressure actuation fluid from the intensifier control passage 56 and to relieve the pressure in the intensifier control passage 56 by exposing it to the hydraulic fluid drain 58. Bias provided by a plunger spring 72 is now able to push the intensifier piston 64 upward. This reduces the pressure of the fuel in the fuel pressurization chamber 66, and hence in the nozzle chamber 48, allowing the bias provided by the check spring 38 to push the check valve member 42 toward its closed position.
However, it takes some time for the high-pressure actuation fluid to move the spool valve member 28 to relieve pressure against the intensifier piston 64. The high pressure actuation fluid in the check control cavity 34 reaches the check control chamber 36 and acts upon the low mass check valve member 42 much more quickly. Even though the nozzle chamber 48 still contains highly pressurized fuel, the combination of the increased pressure in the check control chamber 36 and the bias provided by the check spring 38 overcomes the pressure of the fuel in the nozzle chamber 48. This causes the check valve member 42 to shut immediately, providing a much more abrupt end to the injection cycle than can be obtained otherwise.
Because of this hysteresis affect, the actuator 12 can be turned rapidly on and off to directly control the check valve member 42 by acting on its closing hydraulic surface 40, before the spool valve has released pressure pushing against the intensifier piston 64. Doing this can achieve split injection, that is, two or more injection "shots" in the same fuel injection cycle. In fact, the check valve member 42 can be made to open and close a great many times, as desired, at any time during the injection cycle. For example, this feature can be used to cause a short delay after a "pilot" fuel injection at the beginning of an injection cycle in order to reduce engine emissions or for other reasons.
This seated pin design provides excellent results. To obtain split injection in the same fuel injection cycle using the seated pin valve, the seated pin actuator is turned off to end injection in the first shot, and then turned on again to start injection in the second shot. Controlling the actuation times of the seated pin controls the time interval (separation) between the first and the second shots.
When the separation between two shots is small, inertia of the spool valve helps to maintain pressure on the intensifier piston and the second shot has good injection characteristics. But as the separation increases, the time available for the spool to return and drain the pressure on top of the intensifier increases. In other words, the intensifier top pressure is variable. This causes injection characteristics of the second shot to be a function of the separation.
Test data have also shown that the higher the separation, the more erratic the second shot becomes. These effects are due to the varying levels of pressure on top of the intensifier piston 64. The present invention is directed to addressing one or more of the concerns set forth above.